Have I got this right?

http://www.photography.ca/Forums/mem...th-diagram.jpgThe focal length of the lens is in theory measured from where the light waves cross with pin hole camera to where the film is placed. Because that will depend on film size the amount of seen captured with a 35mm film with 400mm lens will be same as 23.5mm film with 270mm lens as the lens can be closer to the film plane as shown. But with the D-SLR the lens is not closer but the light is projected to non receptive area. This allows the same lens to be used with both film and CCD cameras. In some cases the diameter of the lens will only allow it to be used with smaller film plain so it is marked with effective length. Therefore a lens marked 18mm – 55mm on a 23.5mm CCD can give exactly the same results as a lens marked 27mm – 82mm on a 35mm film (Compare black and green lines). Conversely a 400mm lens from a 35mm film camera becomes a 600mm lens on a 23.5mm CCD camera (Red lines).
Just checking I have got this right before handing in my work?

No ... you spelt 'length' wrong! :)

As far as the rest is concerned ... dunno ... I've never bothered to look into it this closely.

I assume the question is what is the difference between full frame and crop frame cameras. Full frame cameras have a sensor the same size as the 35mm film cameras. Crop frame cameras have smaller sensors and there is a wide variety of these. Your diagram is attempting to explain the differences when using the same lens on different size "film" or sensors.
Try this link for another explanation of the same thing: DSLR Magnification
You an see for yourself where your work and the article's information match up. Hope this helps and isn't more confusing.
Mike

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Originally Posted by Mad Aussie

No ... you spelt 'length' wrong! :)

As far as the rest is concerned ... dunno ... I've never bothered to look into it this closely.

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MA...you spelled "Spelled" wrong! Lol...spelt is a type of flour/grain! :laughing:

Quote:

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Originally Posted by mbrager

I assume the question is what is the difference between full frame and crop frame cameras. Full frame cameras have a sensor the same size as the 35mm film cameras. Crop frame cameras have smaller sensors and there is a wide variety of these. Your diagram is attempting to explain the differences when using the same lens on different size "film" or sensors.
Try this link for another explanation of the same thing: DSLR Magnification
You an see for yourself where your work and the article's information match up. Hope this helps and isn't more confusing.
Mike

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Seems to match up OK. Since it will be part of my exam though it would be good to check first so seems I just need to correct spelling.

Quote:

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Originally Posted by casil403

MA...you spelled "Spelled" wrong! Lol...spelt is a type of flour/grain! :laughing:

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That's only 1 meaning. Spelt is also the past tense of Spell
Spelt | Define Spelt at Dictionary.com

;)

Quote:

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Originally Posted by Mad Aussie

That's only 1 meaning. Spelt is also the past tense of Spell
Spelt | Define Spelt at Dictionary.com

;)

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Lol ya got me...but I'm still taller than you...lol! :evil2:

Poor Eric. At least someone answered his question. Very good link btw mbrager. So what we are saying here, in very basic terms is that a lens that gives a normal view on a 35mm or full frame camera over extends its range on a crop frame camera and gives the appearance of a longer lens. So tecnically, if I have a very good crop frame camera and take an awesome photo of an eagle, and say Micaelaw has a very good full frame camera and takes an awesome photo of an eagle with the same lens from the same distance, he should be able to crop his photo down to the have the subject the same size as mine without losing resolution because technically mine is already a crop of sorts. Does that make sense?
http://luminous-landscape.com/tutori...dslr-mag.shtml

That is my understanding. The second point is if you used a cropped cameras lens on a full screen camera likely the corners of the picture will have no image. With mine at wide angle this is the case.
So a 35mm lens will fit a 23.5mm CCD camera but a 23.5 CCD lens will not fit a 35mm camera without some cropping.

JAS: It makes sense like butter on bread. Unless it makes you want to run out and buy a full frame camera. Except for the part about resolution and cropping which is also related to the number of megapixels and the density of pixels in each camera.
Ericmark:
I use Canon equipment and they manufacture lenses for both full frame and crop frame cameras. They only manufacture one or two full frame cameras anyway. But the full frame lenses will also fit their crop frame DSLR cameras. But the crop frame lenses, called EF-S lenses, are only suitable for the crop frame cameras and won't fit the full frame cameras. So what you are saying in your post is accurate, but the camera manufacturers have already prevented this from being able to happen. Good luck with your exam. When is it?
Mike